This invention relates to a simplified single-stage process for the production of polyamines containing aromatic primary amino groups.
It is known that aromatic isocyanates may be converted into primary aromatic amines by acidic hydrolysis. Unfortunately, the reaction is far from complete, because the amine formed during hydrolysis reacts with unreacted isocyanate to form the corresponding urea. This further reaction cannot be prevented even by using excess strong mineral acid. A more recent example of this process can be found in JP-PS No. 55 007 829.
It is also known that isocyanates can be converted into amines in the presence of acid or basic catalysts, as disclosed for example in N. V. Sidgwick, The Organic Chemistry of Nitrogen, Clarendon Press, Oxford, page 326 (1966) and in J. March, Advanced Organic Chemistry: Reactions, Mechanisms and Structure, McGraw-Hill Book Co., New York, page 658 (1968). Although Sidgwick mentions alkaline hydrolyzability of NCO groups, his comments are very general in nature. March, discloses that the hydrolysis of isocyanates and isothiocyanates to amines can be catalyzed by acids and bases. It is also known, for example in the Curtius or Lossen degradation of acid azides and hydroxamic acids that the intermediate isocyanates may be decomposed with aqueous acid to amine salts. One such process is described, for example, in Organic Syntheses, Coll. Vol. IV, 819 (1963) with respect to the production of putrescin hydrochloride.
E. Mohr, J. Prakt. Chem., 71, 133 (1905) discloses that phenylisocyanate is affected in the cold more quickly by dilute sodium hydroxide than by water. According to C. Naegeli et al., Helv. Chim. Acta, 21, 1100 (1938), phenylisocyanates substituted by electron acceptors (such as nitro groups, halogen atoms or acyl groups) can be converted into the corresponding monoamines over a period of from a few minutes to 1 hour by hydrolysis in moist ether or acetone containing 1% of water (i.e. in the absence of acids or bases) during the reaction. From 2,4-dinitrophenylisocyanate, the corresponding amine is obtained in a yield of almost 100% in hot water (even in the absence of solvent) without any urea-forming secondary reaction.
DE-B No. 1,270,046 describes a process for the production of defined, primary aromatic amines containing polyalkylene glycolether segments, in which reaction products of aromatic diisocyanates or triisocyanates with polyalkylene glycolethers and/or polyalkylene glycolthioethers (preferably those having molecular weights of from 400 to 4000) are reacted with secondary or tertiary carbinols and then subjected to thermal decomposition at high temperatures in an inert solvent (optionally in the presence of acidic catalysts). The high decomposition temperature and the formation of inflammable, readily volatile alkenes which are explosive in admixture with air during thermal decomposition of the urethane are disadvantages of this disclosed process.
DE-B No. 1,694,152 discloses production of prepolymers containing at least two terminal amino groups by reaction of hydrazine, aminophenyl ethylamine or other diamines with an NCO prepolymer of a polyether polyol and polyisocyanate (NCO:NH ratio 1:1.5 to 1:5). Unreacted amine has to be carefully removed in another step because it has a strong catalytic effect on the reaction with polyisocyanates, leading to short processing times.
Another method of synthesizing polyamines containing urethane groups is described in French Patent No. 1,415,317. NCO prepolymers containing urethane groups are converted with formic acid into the N-formyl derivatives which are hydrolyzed to terminal aromatic amines. The reaction of NCO prepolymers with sulfamic acid in accordance with DE-P No. 1,155,907 also gives amino terminated compounds. In addition, DE-B No. 1,215,373 discloses that relatively high molecular weight aliphatic preadducts containing secondary and primary amino groups may be obtained by reaction of relatively high molecular weight hydroxyl compounds with ammonia under pressure at elevated temperature in the presence of catalysts. U.S. Pat. No. 3,044,989 discloses that such compounds may be obtained by reaction of relatively high molecular weight polyhydroxyl compounds with acrylonitrile, followed by catalytic hydrogenation. According to DE-A No. 2,546,536 and U.S. Pat. No. 3,865,791, relatively high molecular weight terminal compounds may also be obtained by reaction of NCO prepolymers with eneamines, aldimines or ketimines containing hydroxyl groups, followed by hydrolysis. Another possibility for synthesizing polyamines containing urethane and ether groups lies in the ring opening which occurs during the reaction of isatoic acid anhydride and diols. Polyamines such as these are described, for example, in U.S. Pat. No. 4,180,644 and in DE-A Nos. 2,019,432, 2,619,840, 2,648,774 and 2,648,825. The poor reactivity of the aromatic ester amines obtained in this way is a disadvantage in numerous applications.
Poor reactivity is also a disadvantage of the compounds containing amino and ester groups which may be obtained in accordance with U.S. Pat. No. 4,504,648 by reaction of polyether polyols with p-aminobenzoic acid ethylester. Those amino compounds which may be obtained, by reaction of polyols with nitrobenzoic acid ethylester and subsequent reaction of the nitro groups to amino groups also exhibit poor reactivity.
The reaction of nitroaryl isocyanates with polyols and subsequent reduction of the nitro groups to aromatic amines is also known (U.S. Pat. No. 2,888,439). The primary disadvantage of such processes lies in the high costs of the reduction step.
It is also known that certain heteroaromatic isocyanic acid esters may be converted into heteroaromatic amines by basic hydrolysis. However, the hydrolysis conditions described by H. John in J. Prakt. Chemie 130, 314 et seq and 332 et seq (1931) for two specific heteroaromatic monoisocyanic acid esters are not only totally unsuitable for the conversion of poly-NCO-compounds into aliphatic and/or aromatic amines, they are also dangerous.
Applicants themselves have proposed multistage processes for the production of polyamines by alkaline hydrolysis of NCO preadducts with excess quantities of base (alkali hydroxides) at low temperatures to carbamates, acidification with equivalent of excess quantities of mineral acids or acidic ion exchanger resins with carbamate decomposition, optionally followed by neutralization of excess quantities of acid with bases, and subsequent isolation of the polyamines (See, for example, DE-A Nos. 2,948,419 and 3,039,600 (believed to correspond to U.S. Pat. No. 4,386,218)).
According to DE-OS No. 3,131,252, the carbamates prepared in a first stage by hydrolysis with alkali hydroxides may be decomposed by subsequent heat treatment to form polyamines.
Single-stage processes are described in DE-OS Nos. 3,223,400, 3,223,398 and 3,223,397. In these processes, "ether solvents" are used together with tertiary amines as catalysts (DE-OS No. 3,223 400): polar solvents, such as dimethylformamide, together with .gtoreq.0.1 part to 100 parts of isocyanate compound) of tertiary amine or with 0.1 to 10 g of alkali hydroxides, alkali silicates, alkali cyanides as catalysts (DE-OS No. 3,223,398); polar solvents, such as DMF, together with 0.01 to 25 wt. % of carbonates or carboxylates as catalysts in DE-OS No. 3,223,397.
These known processes for the production of polyamines are all complicated. Even in the last-mentioned, simpler processes for the convesion of polyisocyanates into polyamines, further simplification would be desirable to enable polyamines to be obtained more economically. The following features of a process of producing polyamines would be advantageous;
(1) no filtration step necessary, PA1 (2) no separation of a tertiary amine catalyst by distillation necessary, PA1 (3) drastic reduction in the necessary catalytic quantity of tertiary amines (DE-OS No. 3,223,398) and PA1 (4) substantially quantitative conversion of NCO groups into NH.sub.2 groups. PA1 (1) water-soluble, aliphatic or cycloaliphatic acid amidines containing from 1 to 10 carbon atoms, for example dimethyl formamide, N-methyl pyrrolidone, dimethyl acetamide, caprolactam, formamide, preferably dimethyl formamide, dimethyl acetamide and N-methyl pyrrolidone: PA1 (2) water-soluble, tetraalkylated aliphatic ureas containing from 4 to 12 carbon atoms, for example tetramethyl ureas or tetraethyl urea: PA1 (3) water-soluble, aliphatic or cycloaliphatic sulfones or sulfoxides containing from 2 to 10 carbon atoms, for example tetramethyl sulfone or dimethyl sulfoxide: and PA1 (4) water-soluble, aliphatic or cycloaliphatic phosphoric acid amides, for example hexamethyl phosphoric acid triamide.